Cold-rolled Steel Research Articles

The Influential Factors of Baking Time in Internal Friction and Bake-Hardening Properties on Low Carbon Steel

This paper aims at exploring the distinctive ways of baking time affecting the hardening degree of the cold-rolled steel. Therefore, with different time span, the annealed sample was baked to test its baking hardening properties. The sample was analyzed micro-structurally after being annealed, pre-deformed and baked. The internal friction was simultaneously measured in terms of different processing conditions during experiments. The following findings are the significant conclusion of the experiments: The important experiment result indicated that when the degree of pre-deformation setting at 5% and the baking temperature at 170°C, the BH value increased but remained unchanged afterwards. Furthermore, when the baking time span was set at 1000 minutes, the BH value reached the maximum but would remain unchanged afterwards. When the degree of pre-deformation was set at 5%, and the baking temperature was set at 17°C with baking time 20 minutes, the SKK peak reached the maximum. When the baking time was 1000 minutes and constantly extended, the height of SKK peak rarely changed. The above experiments are designed to better illustrate and understand the significance of the hardening steel properties for future application in the automobile industry.

Effect of CO2 Laser Fluence on Cladding Geometrical Dimensions Alternations

Geometrical dimensions could play a potential role in the function of laser cladding of nickel-base powder on the cold-rolled carbon steel substrate. The geometrical dimensions and their impact on the efficiency of the process of laser cladding of nickel-base powder (Ni -10wt% Al) on cold rolled 0.2% carbon steel substrate was investigated. This work focused on the effect of laser-specific energy input of CO2laser. The geometrical dimensions of cladding regions are including cladding width, cladding height, depth of dilution, contact angle, dilution area, cladding area, and heat-affected zone dimensions determinations. The laser power (1.8 kW) was used at different traverse speeds (1.5, 3.6, 5, 7.1, 8.6, 12.5 mm/s) with (3mm) laser beam diameter. The feed rate was kept constant after many preliminary claddings at approximately 11 g/min. Fluence values ranged from (48-400J/mm2), and the power density value was (255W/mm2). A minimum dilution percentage (25%) was obtained at the highest fluence value (400 J/mm2). Observations were measured using an optical microscope, scanning electron microscopy, and Image software. Obtained results indicated that the increase in the fluence leads to an increase in height of cladding, HAZ region but lower depth of dilution

Thermal activation process of plastic deformation in Fe–18Cr single-crystal micropillars with high-density dislocations

Micropillar compression testing was performed on bcc solid-solution single-crystal micropillars with two diameter (d) ranges (2–3 and 5–6 μm) prepared on the surfaces of fully annealed and subsequently 10% cold-rolled 18Cr ferritic steel specimens. This was done to investigate the effect of initial dislocations on the plastic deformation of micron-sized crystals. The 10% cold rolling process significantly increased the stress level (provided by an activated single slip system) required to initiate slip in the annealed micropillars with different diameter ranges. In the case of the annealed micropillars, the strain-rate sensitivity (m) of the yield stress becomes lower for larger specimens (the m value decreased from 0.12 to 0.04). However, the 10% cold-rolled micropillars exhibited a much lower strain-rate sensitivity regardless of the specimen size. The activation volume (v*) of the annealed micropillars showed a significant specimen size dependency (v*∝d1.47), consistent with published data on the micropillar compression experiments of single-crystals of the bcc metals and alloys. For the 10% cold-rolled micropillars, the high v* values (88b3 and 112b3) showed a slight dependency on the specimen size (v*∝d0.33). The v* values appeared somewhat higher but were equivalent to those of bulk-size specimens, suggesting that the initial high-density dislocations would provide sufficient sources for dislocation multiplication in the micron-sized specimens under compression. The observed high v* values might be associated with the strong dislocation interactions in the α-(Fe, Cr) solid-solution matrix.

Effect of Coiling Temperature on The Fracture Toughness of Low Carbon Steel.(Dept.M)

The mechanical properties of hot-and cold-rolled steels under various manufacturing conditions have been the subject of several investigations. Fracture toughness, an important design factor for the selection of materials and appropriate design stress levels for fractur resistant structures, did not take much attention in this repect. in this paper, the effect of the temperature at the final steel manufacturing process coiling temperature, on the plane stress fracture toughness for 0.1% carbon rolled step was investigated. Other aspects such as specimen rolling direction and thickness of strip have been considered. Owing lo practical reasons, the normal operating coiling temperature is set at 710°C For the purpose of this study, the conditions at the coilers have been controlled to bring the coiling temperature down to 630°C. Test results indicated that the plane stress fracture toughness for the test material has improved by about 17% when the roiling temperature was brought down from 710°C 630С. Microstructural examination indicated that the grain size or the material decreased with decreasing the coiling temperature. This is known to be responsible for reducing the tendency to nucleate cracks at the grain boundaries leading to increasing the material's resistance to fracture.

Origin of deformation twins and their influence on hydrogen embrittlement in cold-rolled austenitic stainless steel

The effect of cold rolling on hydrogen embrittlement in stable 18Cr–1Mn–11Ni-0.15 N austenitic stainless steels was investigated. Alloy plates were cold-rolled to 15% or 30% reduction, then pre-charged with hydrogen and subjected to tensile testing with slow strain rate. Hydrogen-induced degradation of tensile elongation became increasingly severe with the increase in the degree of cold rolling. During cold rolling, deformation twins with various orientations were actively generated, and twins with specific orientations were vulnerable to hydrogen-induced cracking. Cold rolling also increased the density of defects, and thereby facilitated penetration of hydrogen into the steels. The combination of cracks generated at the twin boundaries, and the promoted hydrogen diffusion caused severe hydrogen embrittlement in the cold-rolled steels.

Ce(SO4)2 as an efficient corrosion inhibitor for cold rolled steel in citric acid solution

The inhibition effect of rare earth salt of Ce(SO4)2 on the corrosion of cold rolled steel (CRS) in 0.50 M citric acid (H3C6H5O7) solution was studied by weight loss, electrochemical technique and surface analysis methods for the first time. The results reveal that Ce(SO4)2 behaves as an efficient inhibitor, and the maximum inhibition efficiency reaches a pleasant value of 97.2% at 20 °C with a little concentration of 0.25 mM. The adsorption of Ce(SO4)2 on CRS surface completely obeys Langmuir adsorption isotherm at 20 - 50°C. Ce(SO4)2 is arranged as a mixed-type inhibitor while mainly retards the cathodic reaction. Electrochemical impedance spectroscopy (EIS) has two time constants. Nyquist diagram contains a depressed capacitive loop at high frequencies followed by an inductive loop at low frequencies. The inhibition of CRS surface by Ce(SO4)2 is evidenced through scanning electron microscope (SEM), atomic force microscope (AFM) and confocal laser scanning microscope (CLSM). The inhibitive mechanism can be mainly attributed to the complexes of cerium (IV) ion with citric anions.

Recrystallisation before austenitization for improved microstructure and properties in automotive steel sheets with high product of strength and elongation

This study investigated the effect of recrystallization before austenitizing transformation (i.e., pre-recrystallization) on the microstructure and properties of 22Mn2Cr cold-rolled automotive steel sheets based on continuous annealing at 700 °C for various holding times. Subsequently, the samples were heated to an austenitizing temperature of ∼850 °C, which led to the formation of a fine austenite grains via nucleation at the dislocations during reheating. The austenite grain size was more refined when samples were pre-recrystallized at 700 °C for several minutes compared to those directly heated to 850 °C, which was attributed to combined grain refinement from recrystallization and austenite phase transformation. This refined austenite grain size led to a finer bainite grain size in the cooled final product. The strength of the steel decreased slightly (∼1200 MPa), but the elongation (∼19%) and product of strength and elongation (∼23 GPa%) were significantly enhanced by the pre-recrystallization treatment.

Microstructure and Mechanical Properties of a Medium-Mn Steel with 1.3 GPa-Strength and 40%-Ductility.

Steel designs with superior mechanical properties have been urgently needed in automotive industries to achieve energy conservation, increase safety, and decrease weight. In this study, the aging process is employed to enhance the yield strength (YS) by tailoring the distribution of V-rich precipitates and to improve ductility by producing high volume fractions of recrystallized ferrite in cold-rolled medium-Mn steel. A reliable method to acquire ultra-high strength (1.0–1.5 GPa), together with ductility (>40%), is proposed via utilizing non-recrystallized austenite and recrystallized ferrite. Similarly to conventional medium-Mn steels, the TRIP effect, along with the mild TWIP effect, is responsible for the main deformation mechanisms during tensile testing. However, the coupled influence of precipitation strengthening, grain refinement strengthening, and dislocation strengthening contributes to an increase in YS. The studied steel, aged at 650 °C for 5 h, demonstrates a YS of 1078 MPa, ultimate tensile strength (UTS) of 1438 MPa, and tensile elongation (TE) of 30%. The studied steel aged at 650 °C for 10 h shows a UTS of 1306 MPa and TE of 42%, resulting in the best product in terms of of UTS and TE, at 55 GPa·%. Such a value surpasses that of the previously reported medium-Mn steels containing equal mass fractions of various microalloying elements.

Modeling and exploiting the strip tension influence on surface imprinting during temper rolling of cold-rolled steel

To produce cold-rolled steel strips with specific mechanical properties and surface roughness typically temper rolling is adopted. In most cases, a uniform roughness pattern on the strip surface is mandatory. Due to the wear of the textured work rolls, their surface roughness (Ra) continuously reduces during the process, which should be accounted for process control. However, conventional temper rolling systems fail to guarantee a uniform surface roughness. In this work, the influence of strip tension on the imprinting of surface roughness during temper rolling is analyzed based on a multi-scale FE modeling concept to explore new ways for surface roughness control. This is done in simulation where, a macroscopic rolling model incorporating strip tension is coupled to a mesoscopic imprinting model and both models are validated using copper rolling trials. The influence of different thickness reductions, strip tensions and incoming strip's surface roughness on imprinting is modeled and compared. The numerical results reveal that a higher strip tension decreases the roughness transfer, which presents potential to control the roughness transfer ratio without changing other process parameters like the prescribed thickness reduction in the future.

Testing the Cross-Sectional Microhardness in Sheets with A 0.08% Carbon Concentration

The research team studied the hardness of cold-rolled sheets of varying thicknesses containing 0.08% carbon. Greater thickness correlated with lower mean hardness. The hardness was found to drop in the middle of a plate and to increase gradually towards the edges. This pattern was observed regardless of the thickness of thin cold-rolled sheet steel. The change in hardness may indicate uneven accumulated strain in the sheets rolled to a desired value. Pre-hardened sheets were analyzed to find whether the hardness was homogeneous through the thickness. The material was hardened by axial tensioning. Analysis showed that at greater accumulated strain, the through-thickness hardness was affected as well. However, the difference was less pronounced at the edge as well as in the middle of sheets. The paper shows graphs of the hardness distribution through thickness.

Prospects of Production and Application of Cold-Rolled Electrical Steel for Magnetic Cores of Rotary Electric Machines

Prospects of Production and Application of Cold-Rolled Electrical Steel for Magnetic Cores of Rotary Electric Machines

Investigations on Magnetic and Corrosive Characteristics of Thin Cold-Rolled Nonoriented Electrical Steel Sheets Post Gas Tungsten Arc and Laser Welding

Abstract Thin sheets (0.5 × 10−3 m) of cold-rolled nonoriented (CRNO) electrical steel are widely used for rotating electrical machines. Gas tungsten arc (GTA) and, recently, laser welding are used for welding M-43 grade CRNO steel. The performance of CRNO is thus explored because of changes in low-carbon, high-silicon content and thin insulation coatings post welding. The welding current for GTA varied from 30 to 110 A, whereas a laser of 800 W was used to estimate the heat affected zone (HAZ), fusion zone (FZ), and weld characteristic ratio. Ferritic phases with polygonal grain size, percent silicon content, magnetic losses, and welded corrosive samples corrosion rate (in mils penetration per year) are compared with the base material (average grain size 55 ± 12 μm). Five different corrodent (NaCl, NaOH, HCl, H2O, H2CO3) environments were created for 2,000 h as per ASTM B895-16(2020)e1, Standard Test Methods for Evaluating the Corrosion Resistance of Stainless Steel Powder Metallurgy (PM) Parts/Specimens by Immersion in a Sodium Chloride Solution, and ASTM G31-72(1999), Standard Practice for Laboratory Immersion Corrosion Testing of Metals standards. The GTA weld samples revealed much-increased weld geometry with welding current, and a significant increase in grain sizes up to 189.2 ± 4 μm for GTA and 187 ± 3 μm for the laser sample near the weld zone is observed. Microhardness variation is found to be in the range of 55 HV for GTA and 51 HV for laser samples in the FZ region with reference to the base metal hardness of 227 HV. In addition, the increase in core loss of 58.72 % for GTA and 39.82 % for laser samples with reference to nonwelded samples is observed.

Study of thermal resistance of cold mixtures with clay addition

The article analyzes the results of heat resistance of cold-harmful mixtures with the addition of clay. The article presents the results of an experimental laboratory study of the properties of samples from CTS, obtained by various methods. The scientific novelty of the technology lies in the fact that the technology of casting in cold-rolled steel ensures high quality of the casting surface, the absence of gas defects and blockages in the casting. The selection of the composition and technological parameters for the manufacture of the mold, contributing to the production of high-quality defect-free castings, will significantly reduce their cost, which will have a positive effect on the economy of our country. The study of the change in density over time depending on the applied load was studied in a series of experiments. The density of the mixture was determined every thirty seconds during the entire time of the formation of the dispersed medium. These experiments showed that at the beginning of the formation of the shell, its density increases significantly. In works on the thermal stability of polymers, the general laws of thermal decomposition and carbonization of cyclic, spatially crosslinked hot curing polymers were investigated and it was shown that the kinetics of destruction, the composition of gaseous products, the amount of coke formed and its properties depend on the properties of the initial polymers - the degree of crosslinking of molecular chains, chemical structure, the presence of impurities of catalysts and other curing conditions, as well as the heating conditions - speed and temperature. The article summarizes some of the results of the study, which is most appropriate for thin-walled steel castings to use the following mixture composition: filler - quartz sand; binder - clay of the Kazakhstani deposit, epoxy resin, hardener.

The precipitation behavior and its effect on mechanical properties of cold-rolled super-ferritic stainless steels during high-temperature annealing

The precipitation behavior, microstructure evolution and mechanical properties of a cold-rolled 27.6Cr–3.7Mo–2Ni ferritic stainless steel during high temperature annealing treatment were investigated. Experimental results demonstrated that the cold rolled microstructure was characterized by orientation-dependent heterogeneity, and many shear bands were found in the <111>//ND (normal direction) orientation grains. The elongated deformation microstructure gradually changed into equiaxed grains and three kinds of interphases including σ-phase, χ-phase and Laves phase were observed as the annealing temperature increased from 850 to 1000 °C. After annealing below 1000 °C, the σ-phase and χ-phase were observed to be located at grain boundaries, near the TiN particles as well as along with shear bands in grains, whereas the Laves phase distributed dispersedly in grains. After annealing at 1000 °C, both the σ-phase and χ-phase were almost completely dissolved, while the nanoscale Laves phases at grain boundaries were dominant. The grain boundary Laves phase precipitation at high temperature was attributed to the Nb segregation induced by cold rolling deformation. The σ-phase precipitation kinetics was calculated based the Johnson–Mehl–Avrami equation, and the fastest precipitation kinetics appeared at 850 °C with the activation energy of ~176.7 kJ·mol−1. The Vickers hardness, ultimate tensile strength and yield strength values decreased while the elongation value increased with increasing annealing temperature. The breakage pattern transformed from brittle to ductile fracture as the annealing temperature increases from 850 to 1000 °C.

Corrosion behavior of cold-rolled and post heat-treated 316L stainless steel in 0.9wt% NaCl solution

The effect of cold rolling and post-rolling heat treatment on the microstructural and electrochemical properties of the 316L stainless steel was investigated. Two-pass and four-pass cold-rolled stainless steel specimens were heat-treated by annealing at 900°C followed by quenching in water. During the cold rolling, the microstructure of the as-received specimen transformed from austenite to strain-induced α’-martensite due to significant plastic deformation that also resulted in significant grain elongation (i.e., ∼33% and 223% increases in the grain elongation after two and four rolling passes, respectively). The hardness of the heat-treated as-received specimen decreased from HV 190 to 146 due to the recovery and recrystallization of the austenite grain structure. The cyclic polarization scans of the as-rolled and heat-treated specimens were obtained in 0.9wt% NaCl solution. The pitting potential of the four-pass rolled specimen was significantly increased from 322.3 to 930.5 mV after post-rolling heat treatment. The beneficial effect of the heat treatment process was evident from ∼10-times-lower corrosion current density and two-orders-of-magnitude-lower passive current density of the heat-treated specimens compared with those of the as-rolled specimens. Similarly, appreciably lower corrosion rate (3.302 × 10−4 mm/a) and higher pitting resistance (1115.5 mV) were exhibited by the post-rolled heat-treated specimens compared with the as-rolled 316L stainless steel specimens.

Recrystallization behaviour of IF steel at the interface of Al junction

The recrystallization behavior of an IF steel was investigated at the interface with aluminum junction, using cold-rolled IF steel sheets with high recrystallization temperature. In the region surrounded by the tongue-like η phase, recrystallization of the steel was fast at first glance, and the equiaxed structure was formed, but actually, it had a subgrain structure. The η phase grew preferentially to the c axis, and the growth of the η-Fe2Al5 phase distorted the surrounding iron due to the difference in the molar volume; compressive deformation was expected in the a-axis and b-axis directions, and tensile deformation was expected in the c-axis. The growth of η phase obviously changed the recrystallization behavior of the IF steel. The development of γ-fiber crystalline texture (<111>/ND), which was a typical recrystallization texture of IF steel, was not observed in the region surrounded by η phase.

Observation of Inhomogeneous Deformation in a Cold-Rolled Ti-added Ultra-Low Carbon Steel using High-Precision Markers Drawn by Focused Ion Beam

The development of deformation inhomogeneities in ultra-low carbon steel due to cold rolling has been investigated by observation of the longitudinal plane at chosen sites of a rolled sheet using SEM and SEM-EBSD techniques. Particular attention has been paid to the development of strain distribution in the crystals. The microstructures and the orientation distribution in the longitudinal plane of a sheet rolled to a 60% reduction in thickness were observed, and some grains with preferred orientation such as α-fiber and γ-fiber were selected. In order to examine the local strain distribution of these grains due to cold rolling, high-precision dot markers, 0.3μm in diameter, were drawn using a focused ion beam. Then, before being subjected to additional rolling, the sheet was fitted into a frame made of the same steel under a plane strain condition. Using the marker method, the local displacement of the grains due to cold rolling has been directly measured.

Influence of Mo–Nb–Ti additions and peak annealing temperature on the microstructure and mechanical properties of low alloy steels after ultrafast heating process

Abstract The influence of the heating rates from 10 to 1000 °C/s and annealing temperatures on the microstructure and mechanical properties of two 0.2%C, 1.9%Mn, 1.4%Si cold-rolled steels with and without the addition of carbide-forming elements (Mo, Nb, and Ti) have been investigated. Results show that the increase of the heating rate above 100 °C/s refines the parent austenitic grains in both alloys. The increment of the heating rate led to carbon heterogeneities in the austenite, which after subsequent cooling promoted the formation of a complex mixture of fine-grained constituents. As expected, at the lower heating rates the presence of Nb and Ti-rich carbides and carbonitrides controls the austenite grain growth during the annealing treatment. The tensile test results reveal that high heating rates do not have a significant influence on the tensile strength of the alloy with carbide-forming elements. On the other hand, both the ultimate tensile strength (UTS) and total elongation of the alloy without carbide-forming elements decrease, due to the formation of bands of ferrite and high carbon martensite. However, samples treated at heating rates above 100 °C/s show a combination of UTS in the range of 1400–1600 MPa, and 12–18% of total elongation. The results suggest that the microstructure heterogeneity obtained after high heating rates, especially the ferrite content, has the major effect on the mechanical behavior of the studied steels.

Aniline pentamer-modified reduced graphene oxide/epoxy composites as anticorrosion coatings

A series of composite coatings that consist of electroactive epoxy thermoset (EET) containing pendant aniline pentamer and reduced graphene oxide (rGO) platelets was prepared, characterised and applied as anticorrosion coatings. Diamine monomer with pendant unilateral amino-capped aniline pentamer (DAAP) was prepared by reacting the as-prepared aniline pentamer (AP) with 2,6-difluorobenzoyl chloride then reacted with 4-aminophenol. The chemical structure of AP, and DAAP was characterised by FTIR, NMR and mass spectroscopy. The EET composite coatings were prepared by reacting DAAP with epoxy resin in the presence of suitable feeding ratio of GO/rGO at specific programmed heating and then characterised by TEM. The corrosion protection of cold-rolled steel electrode coated with Non-EET (NEET), EET, GOEET and rGOEET was investigated by performing a series of electrochemical corrosion measurements (such as Tafel, Nyquist and Bode plots) in saline condition. Notably, the corrosion protection of coatings revealed the following trend: rGOEET＞GOEET ＞ EET ＞ NEET over a short- and long-term anticorrosion performance. The best anticorrosion performance of rGOEET composite coatings resulted from the synergistic effect of the excellent O2 barrier property, caused by the efficient dispersion of rGO in the EET matrix, and the formation of passive metal oxide layers induced by the pendant AP existing in EET coating. Moreover, the proposed composite showed excellent mechanical properties. This method of pendant aniline pentamer cold open the door for further investigations of other pendant electroactive polymers towards efficient coating materials.

Enhancement of the tensile properties and impact toughness of a medium-Mn steel through the homogeneous microstrain distribution

In this study, we reveal that strain partitioning control is an essential technique to improve the mechanical response of medium-Mn steels by the micro digital image correlation analysis. An Fe-12Mn-0.06C-3Al (wt%) steel, which shows transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), was used as a model alloy. Two alternative austenitization treatments at 850 °C (LA) or 1100 °C (HA) for 10 min were conducted on cold-rolled steels to achieve different sizes of prior γ grains before intercritical annealing (IA) (600–660 °C for 1 h). The samples, which were annealed at the same temperature, showed two-phase nanolaminate microstructures of tempered martensite (α'temp) and retained austenite (γR) with similar phase fraction regardless of the austenitization temperature. When annealed at the same temperature, the LA specimen showed smaller colonies of γR grains with the same crystallographic orientation and spatial alignment as compared to the HA specimen. The LA specimen revealed higher strength, ductility, and toughness than the HA specimen. The main reason for this mechanical response is related to microstrain localization during deformation. Due to the appearance of colonies of γR with the same crystallographic orientation and spatial alignment, the microstrain tends to be localized in colonies with favorable orientation and alignment to the tensile axis apart from strain partitioning to the γR. The LA specimen with smaller colonies of γR exhibits a more homogeneous microstrain distribution relative to the HA specimen. This results in more global TRIP and TWIP behaviors during plastic deformation of LA specimen, leading to the improved mechanical responses.